What data type is valid for piecewise functions?

I am trying to graph a simple piecewise function.

Basically, I am trying to graph:

for x < 0, y = -x, 
for x>0, y = x. 

My code looked like this:

x = -10:1/100:10;
y = piecewise(x<0, -x, x>0, x);
plot(x,y,'r')
axis([-10 10 -10 10])

But when I attempt to do it using the piecewise command, I get this message:

Undefined function 'piecewise' for input arguments of type 'double'.

So after that I tried using the cast command to change the data type.

Then, my code looked like this:

x = -10:1/100:10;
b = cast(x, 'single')
y = piecewise(b<0, -b, b>0, b);
plot(b,y,'r')
axis([-10 10 -10 10])

and once again, I got

Undefined function 'piecewise' for input arguments of type 'single'.

And I tried this for all data types and it didn't work. What am I missing?

Here is my code:

% This plots the x-axis
x = -100:1/100:100;
y = 0*x;
plot(x,y,'k')

hold on 

%This plots the y-axis
x = -100:1/100:100;
y = 9999*x;
plot(x,y,'k')

hold on 

%This is the graph 

x = -10:1/100:10;
y = piecewise(x<0, -x, x>0, x);

plot(x,y,'r')
axis([-10 10 -10 10])

[dpb]

piecewise is part of Symbolic Toolbox -- looks like you don't have it; the message is saying it can't find the function piecewise; in this case the input argument type part of the message is a distraction.

What does

which -all piecewise

return?

[Chase Reiter]

Where should I implement "which -all piecewise" ?

[Chase Reiter]

It appears as though I have already installed Symbolic Toolbox

[Alan Stevens]

Why not just:

x = -10:1/100:10;
y = abs(x);
plot(x,y,'r')
axis([-10 10 -10 10])

[Chase Reiter]

Alan Stevens,

This script is just a tester for a bigger project I am working on. The focus of this project depends upon me using a piecewise function so I have to use the piecewise command. In the end, I won't end up using this code anyway, it's just a tester.

[dpb]

Type it in at the command line to see what MATLAB returns for the piecewise function resolution.

[Chase Reiter]

When I typed which -all piecewise into the command line, I got:

C:\Program Files\MATLAB\R2019a\toolbox\symbolic\symbolic\@sym\piecewise.m % sym method

Answer 1

[Chase Reiter]

The reason it wasn't working was because I wasn't making my function symbolic.

Here is the correct code. It works perfectly.

% This plots the x-axis
x = -100:1/100:100;
y = 0*x;
plot(x,y,'k')

hold on 

%This plots the y-axis
x = -100:1/100:100;
y = 9999*x;
plot(x,y,'k')

hold on 

%This is the graph 

syms y(x);
y(x) = piecewise(x<0, -x, x>0, x);

fplot(y)
axis([-10 10 -10 10])

Answer 2

[dpb]

syms x
y = piecewise(x<0, -x, x>0, x);
fplot(y,'r')
axis([-10 10 -10 10])

[Chase Reiter]

That also works